After trading for many years we are now very careful about letting cars go out without payment but we still get caught out at times.
We done a clutch recently on a van,customer insisted on test drive before payment,(shorten long story)sent out mech with customer,this customer then drove like a lunitic,threatened mech and dumped him out on the road,police very good and quickly made arrest,after giving loads of statements CPS decided not to prosicute,i have now taken matter higher and awaiting outcome but hold out little hope in justice.In the past i have knocked on doors to get payment and they have threatened to call police or threatened me,not too worried about myself but after building up a business over many years where we have customers cars and sales cars in the yard i have a lot to loose if they decide to visit my premises one night.
So you have to weigh up the pros and cons,in the past we have used all means suggested in the above posts and more,often to no avail,it just costs me more money,time and stress.I now just go as far as i reasonably can then write it off.Hopefully our paths will (and do)cross again.
Hope this does not sound defeatist but i try to be realistic
Regards Tony